Semiconductors of the III-N type, that is having the general formula AlxGayIn1-x-yN where 0≦x≦1, 0≦y≦1 and x+y≦1, and GaN in particular, have characteristics which make them very attractive for the optoelectronic field, power components and radio frequency applications.
However, the development of these applications is slowed by the techno-economic limits of the substrates.
Indeed, device manufacturing depends generally on the transfer to a supporting substrate of a thin layer taken from a donor substrate, which is a massive substrate of high quality III-N material suited to the intended application.
The SMARTCUT® process in particular is a well-known transfer technique, which consists generally of implanting a dose of atomic or ionic species into a donor substrate, so as to create in it an embrittlement zone at a predetermined depth, thus delimiting the thin layer to be transferred, sticking the donor substrate onto a support substrate or receptor substrate, and causing the donor substrate to break at the embrittlement zone, thus allowing the detachment of the thin layer stuck to the receptor substrate. In this technology, the separation of the layer to be transferred and its detachment from the donor substrate are obtained by the creation of crystal defects such as platelets and holes induced by the implanted species and their coalescence in a plane by thermal activation.
However, in the case of substrates made of III-N material, implantation requires doses of atomic or ionic species that are five to ten times greater than in silicon, which results in a considerably increased process cost.
A method for manufacturing a thin plate of a semiconductor with a wide band gap which can be transferred to a handling substrate in as thin a form as possible without damaging the substrate is described in document WO2010/067835.
The method includes an ion implantation from the surface of a wide band-gap semiconductor in order to form an ion implantation layer, a step of applying a surface activation treatment to at least the aforementioned surface of the handling substrate, a step of bonding the surface of the wide band-gap semiconductor to the surface of the handling substrate to obtain a bonded body, a step of applying a heat treatment to the bonded body at a temperature of 150 to 400° C., and a step of exposing the ion implantation layer to visible light to embrittle the ion implantation layer and transfer the wide band-gap semiconductor layer onto the handling substrate.
As stated above, the light exposure step is intended to embrittle the ion implantation layer, so this technique is fully akin to the SMARTCUT® process mentioned earlier, including the consequent cost considerations. Indeed, implantation is carried to embrittle the layer of interest, then heat treatment to activate the creation of crystalline defects, and to finally fracture the layer of interest layer at the crystalline defects.
Further, the article “Fabrication of light emitting diodes transferred onto different substrates by GaN substrate separation technique” (Y. Kunoh et Al./Phys Status Solidi C7, N) 7-8, 2091-2093 (2010)/DOI10.002/pssc200983576)” describes a technique in which two stacked layers are created, i.e., a layer that absorbs visible light covered by a layer that is “transparent” to the same light. The properties of the buried layer, presented as a sacrificial layer, are modified.
This modification is carried out immediately following fabrication of the layer, that is to say before it is covered by the transparent layer.
It is carried out by annealing, which “thermally decomposes” the layer.
This decomposition performed before the formation of the transparent layer is presented as making it possible to “avoid ending up with a thermally damaged surface layer (LED).”
Growth of the transparent layer on the sacrificial layer is then accomplished by epitaxy, then irradiation with a light allowing transfer to the sacrificial layer.
It therefore seems that the annealing allows the initiation of the decomposition of the sacrificial layer, making it more absorbent, which is then completed by irradiation with light.
This therefore involves the decomposition of a layer which will subsequently be covered by epitaxy. This constitutes a major drawback, because the surface of the sacrificial layer is degraded by these treatments, so that it no longer has an optimal crystal matrix for epitaxy.
One of the objectives sought by the present invention is particularly to develop a preparation method for a substrate made of semiconductor materials, with the aim of detaching a layer of the substrate, which does not have the limitations of the existing methods and is less costly.